Sulfuric acid polymerization of diorganosiloxanes



March 2, 1948.

R. R. MCGREGOR ET AL SULFURIC ACID POLYMERIZATION OF DIORGANO SILOXANESFiled llarCh 30, 1943 a0 40 loans 07- 220 Can:

Him-mp Patented Mar. 2, 1948 SULFURIC ACID POLYMERIZATION FDIORGANOSILOXANES Rob Roy McGregor,- Verona, and Earl Leathen Warrick,Pittsburgh, Pa., assignors to Corning Glass Works, Corning, N. Y., acorporation of New York Application March 30, 1943, Serial No. 481,143

This invention relates to new compositions of matter, their preparationand uses and, more particularly, to organo-silicon polymers and methodsof preparing them.

This application is a contlnuation-in-part of our copending applicationSerial Number 460,830, filed October 5, 1942. e

The present invention is concerned with a method of further polymerizingorgano-silicon oxide polymers and with the products derived therefrom.Organo-silicon oxide polymers are compounds which contain organicradicals attached to silicon through a carbon atom and whose siliconatoms are joined to other silicon atoms by oxygen atoms, thus Si-O-Si.They may be prepared by the hydrolysis of hydrolyzable organo-silicanesand condensation of the hydrolysis products. Furthermore, hydrolysis ofa mixture of difi'erent hydrolyzable organo-siliv canes andco-ccndensation of the hydrolysis products produces organo-siiicon oxidecopolymers which are within the scope of our invention. In the lattercase, a hydrolyzable silicane which contains no organic radicalsattached to silicon through a carbon atom, such as silicon tetrachlorideor ethyl orthos'ilicate, may be included along with the hydrolyzableorgano-silicanes. By hydrolyzable organo-silicanes we mean derivativesof SiH4 which contain readily hydrolyzable radicals such as hydrogen,halogens, amino groups, alkoxy, aroxy and acyloxy radicals, etc., theremaining valences of the silicon atoms being satisfied by organicradicals that are joined to the silicon atoms through carbon atoms suchas alkyl, substituted alkyl, aryl, substituted aryl radicals, etc.

Hydrolysis of the above silicanes or mixtures thereof is generallyconcurrently accompanied by condensation to a greater or less degreedepending upon the conditions of hydrolysis and the particular silicanesinvolved. As a result of the hydrolysis and concurrent condensation,organo-silicon oxide polymers or organo-siloxanes (as they are nowcommonly called) are produced which are partially or completelycondensed and which have on the average up to and including threeorganic radicals attached to each silicon atom. The polymers so obtainedvary in character, some being oily liquids, others being crystallinesolids or gels. They also vary in the ease with which they may befurther polymerized by heat since they diifer in the number of activefunctional groups retained as a result of incomplete hyrolysis andcondensation. Those which are only partially condensed may be convertedto 6 Claims. (Cl. 260-607) higher polymers and even to solids by heatalone or even by standing at room temperature by virtue of thecompletion of condensation. On the other hand, those organo-siloxaneswhich approach complete condensation are extremely resistant to furtherpolymerization by heat alone. These substantially completely condensedpolymers are not limited to those which are of high molecular weight butmay be polymers of low molecular weight as well. For example, thecondensed hydrolysis products of the di-organo-silicanes are essentiallycompletely condensed even in the low polymeric stages and existgenerally as liquids in the trimeric form with polymers as high as thehexamer being reported in only rare instances. Since the higher polymersof these organo-silicon oxide compounds, and particularly the higherpolymers of the substantially completely condensed compounds, have beenfound to possess properties which adapt them to many industrialapplications as will be described below, it is highly desirable toprovide a method of further polymerizing the organo-silicon oxidepolymers to higher polymeric compositions, that is, to increase theiraverage molecular weight.

The primary object of this invention is to provide a method ofpolymerizing the hydrolysis products of hydrolyzable organo-silicanes ormixtures thereof.

Another object of our invention is to provide a method of furtherpolymerizing an organo-siloxane having on the average less than threeorganic radicals attached through carbon atoms to each silicon atom.

Another object of our invention is to provide a method of furtherpolymerizing a substantially completely condensed liquid hydrolysisproduct of a silicane of the type RzSiXa, where each R is an organicradical which is joined to the silicon atom through a carbon atom andeach X is a hydrolyzable atom or group.

Still another object of the present invention is to provide a method ofpolymerizing a substantially completely condensed liquid hydrolysisproduct of a mixture comprising essentially a diorgano-substitutedsilicane to a polymeric composition which is substantially free ofpolymers having less than seven silicon atoms per molecule.

Another object of our invention is to provide a method of polymerizingto a heat convertible state a liquid organo-siloxane having on theaverage less than three organic radicals attached through carbon atomsto each silicon atom.

A further object of our invention is to provide a method of polymerizingto an infusible resinous A still further object of our invention is toprepare organo-siloxanes of high average molecular weight which aretack-free resins.

' In accordance with our invention, we have provided a method ofpreparing an extremely useful polymeric composition from the hydrolysisproduct of a hydrolyzable organo-silicane or of a mixture ofhydrolyzable silicanes which comprises treating the hydrolysis productwith sulphuric acid under polymerizing conditions until a polymericcomposition having the properties desired is obtained. If desired, thesulphuric acid may be added during the initial hydrolysis andcondensation of the sllicane or mixture of silicanes since we have foundsulphuric acid to be an effective condensation agent as well as catalystfor promoting the rearrangement of Si-O-Si bonds. It is important,especially in the case of the liquid hydrolysis products which aresubstantially free of active functional groups, that the sulphuric acidbe maintained in intimate and continuous contact with theorgano-siloxane until a polymeric mixture of the desired averagemolecular weight is obtained, for we have found that an appreciableincrease in average molecular weight does not occur until the polymerhas been so treated for some time. After this induction period, theviscosity and average molecular weight of the treated material risesrapidly until a stage of polymerization is reached where the sulphuricacid is no longer necessary to promote polymerization but heat in thepresence of air is sufllcient to convert the polymer to a tack-freeresinous solid. Those organo-siloxanes which are initially onlypartially condensed, of course, do polymerize by heat alone but we havefound that treatment of these siloxanes in accordance with our inventionnot only increases the rate of polymerization but inmany instancesproduces flexible resinous solids instead of the mechanically weak gelsordinarily obtained by heat alone. In carrying out our method, we havefound that the addition of water in the form of steam during thepolymerization process aids in speeding up the polymerization. Theparticular concentration and quantity of acid employed and the optimumtemperature for carrying out the polymerization are conditions whichvary with the organo-siloxane being treated and also with the type ofproduct desired as will be readily apparent from the examples givenbelow. However,

we prefer to use aqueous acid or at least to have water present to someextent if concentrated acid is used since too rigorous treatment withsulphuric acid will result in excessive oxidation of the silicone. Wealso prefer to carry out the polymerization with sulphuric acid at atemperature between about 100 C. and about 250 0. although lowertemperatures have been employed with success. Upon completion of theprocess the sulphuric acid may be removed but we have found that incertain instances its continued presence does no harm and in fact mayimprove the properties of the product for certain purposes.

In general, any liquid organo-siloxane having on the average less thanthree organic radicals is, treatment in accordance with our method willresult in an increase in average molecular weight. Our method is notgenerally applicable to those polymers having three organic radicalsattached to each silicon atom, that is, the dimeric ethers, since theonly way the latter can polymerize is by removal of groups. However, itis to be understood that groups may be removed to some extent by thesulphuric acid treatment but it is believed that polymerization of thecondensed organo-siloxanes is primarily due to a rearrangement of theSi-O-Si bonds under the influence of the acid.

We have found that sulphuric acid is greatly superior to other catalystsnot only in speeding up the polymerization of the organo-siloxanes butin producing products with more desirable properties. By the use ofsulphuric acid, liquid polymers may be obtained which reach extremelyhigh viscosities without gelation and tack-free resinous solids ofexcellent mechanical properties may be obtained. We have further foundthat by using sulphuric acid as a polymerization catalyst a greateryield of polymerized product is obtained than with other acid catalysts.is probably due to the rapidity of the polymerization whereby the lowermolecular weight polymers which are more volatile are quickly convertedto the more viscous and accordingly less volatile higher molecularweight polymers. Another advantage in employing sulphuric acid arisesfrom its relatively low volatility thereby insuring continuous andintimate contact with the treated organo-siloxane.

For better understanding of our invention, reference should be had tothe accompanying drawing in which the effect of sulphuric acid on phenylethyl silicone is shown and to the following examples.

Exmul Dimethyldiethoxysilicane was mixed with 34% by volume of sulphuricacid. After being stirred for five minutes, its viscosity was 720Saybolt seconds at 30 C. Another sample of the dimethyldiethoxy silanewas hydrolyzed in the presence of concentrated hydrochloric acid andthen refluxed; its viscosity was only 49.2 Saybolt' seconds at 30 C.after 4 hours of such treatment.

EXAIIPLBZ A mixtureof cc. of dimethyldiethoxysilicane, 50 cc. of 85%sulphuric acid and 2 cc. of 30% hydrogen peroxide (for maintainingsolution clear) was stirred for five minutes. A viscous oil wasproduced. This was heated under a vacuum (150 mm.) and stirred by meansof a stream of air. The temperature was kept at -120 C. for 6 hours andat -200 C; for 4 hours. The resulting polymer which was very viscous wasdissolved in benzene. A tape consisting of woven glass fibers was dippedinto the benzene solution and upon withdrawal wasbaked for 20 hours at0., for 48 hours at 250 C., and for 100 hours at 300 C. The resultingcoated tape was non-tacky and flexible.

Exmnx 3 A,mixture of 300 cc. of dimethyldiethoxysilicane, cc. of 95%ethyl alcohol and 150 cc. of concentrated hydrochloric acid was refluxedfor four hours. An oil was separated from the mixture having a viscosityof 34 Saybolt seconds. To a sample of this oil 4 drops of concentratedsulphuric acid (about 2% by weight) were added. Air was then bubbledthrough the oil at 30 This 5 C. for 2 hours. Its viscosity Wasdeterminedto be 720 seconds. It was further heated on a water bath for two hourswith air bubbling through. Lower boiling fractions which were distilledofi the product amounted to about 2% by weight. The residue had aviscosity of 4300 Saybolt seconds.

Exmrn 4 10 cc. of 95% ethyl alcohol and'1.4 cc. of 1.0 N

sulphuric acid was held at 30 C. for 21 hours. 3 cc. of carbitol'acetate were then added to the mixture in order to facilitate theremoval of alcohol and water in subsequent desiccation. The entiremixture was transferred to an aluminum dish in a desiccator where it wasmaintained under vacuum for 24 hours. The alcohol and water were therebyremoved. The aluminum .dish and its contents were then placed in an ovenat 100 C. for 3 days; at 175 C. for two days and at 200 C. for a day.The product was a horny resin while a blank which had been subjected tothe same treatment without any sulphuric acid was completely shatteredand had lost 3% times as much weight as the sulphuric acid treatedsample.

EXAMPLE 5 A mixture of 726 cc. of methyltriethoxysilicane and 429 cc. ofdimethyldiethoxysilicane was poured into 570 cc. of 2 N hydrochloricacid which had been cooled to 5 C. The reaction mixture was kept at 05C. for 3 hours. A viscous liquid precipitated which was separated andallowed to stand at 0 C. for 24 hours. A sample of this liquid washeated at 285 C. until it solidified to a resin which was very brittleand cracked. Another sample of the viscous liquid was dissolved intoluene to which drops of concentrated sulphuric acid were added. Thesolution was refluxed for 45 minutes. The solvent was distilled oil andthe residue heated to 280 C. A non-brittle non-tacky resin was obtained.

EXAMPLE 6 Table Viscosity Saybolt Sulphuric Sam e Time of Heating 4hours 7 hours 13 hours EXAMPLE 7 Phenyl ethyl silicon dichloride washydrolyzed to an oil which was established to consist primarily of thetrimer of phenyl ethyl silicone. A charge containing 346 lbs. of thitrimer was heated to a temperature of 190 C. over a period of hours.Five hundred grams of a 50% aqueous sulphuric acid solution was addedover 6 a period of two hours. Steam was then introduced very slowly intothe mixture. After eight hours at 190-200 C., the temperature was-raisedto 220 C. and held there for the remainder of the polymerization whichrequired a total of 48 hours at 220 C. An additional 400 g. of 50% acidwas added in three shots at the end of 27. 33. and 50 hours after thefirst addition to replace the acid distilled out. During the passage orthe steam the viscosity Of the mixture increased and was tested atintervals by withdrawing samples of the mixture, dissolving each samplein an equal weight of toluene. and measuring the viscosity oftheresultant solution. When the viscosity in the toluene solutionreached 65 centipoises, the charge was cooled to 100 C. and 220 lbs. oftoluene added and stirred until the viscous polymeric mixture wascompletely dissolved. The solution was then filtered with filter cellthrough a filter press and concentrated to 314 lbs. of a 70% solidcontent. This toluene solution serves as an excellent coatingcomposition for impregnating the interstices of glass fibre insulatingtape, the toluene being evaporated by heat leaving a film which set to atough adherent coating when heated in the neighborhood of 250 C. Thefigure in the drawing is a graph which shows the change in viscosity ofthe heated mixture with time. The first eight hours at 200 C. areomitted. It will be observed that during the greater part of the time ofheating the increase in viscosity is extremely slow but that when theviscosity does start to rise it increases very rapidly so that most ofthe increase is efiected in a very short time.

EXAMPLE 8 A mixture of ethyl silicon trichloride, phenyl ethyl silicondichloride and diphenyl ethyl silicon monochloride in the molar ratio of1-8-2 respectively was dissolved in ether and hydrolyzed by mixing withwater. The ether solution of the resulting copolymer was washed free ofhydrochloric acid, and the ether removed by distillation. The resultingether free copolymer was then polymerized with .2% by weight of H2804while blowing with steam. After 30 hours, the product was a resinoustacky material, soluble in toluene and having a viscosity in 50%solution of 420 centistokes at 25 C. Applied from a toluene solution toglass fibre tape it dried (after removal of solvent) in 3 hours ofbaking at 250 C. to a heat resistant, tack-free resin.

Exammz 9 A mixture of ethyl silicon trichloride, phenyl silicontrichloride, phenyl ethyl silicon dichloride, diphenyl silicondichloride, diethyl silicon dichloride and' diphenyl ethyl siliconmonochloride (prepared by reaction of silicon tetrachloride, phenylmagnesium chloride and ethyl magnesium chloride in molar ratio of 1-1-1at 20 C.) was dissolved in ether and hydrolyzed with water. The ethersolution was washed free of acid and the ether removed by distillation.The resulting copolymer material was polymerized to-a viscous, tackymaterial by heating at 220 C. with .2% by weight of H2804 while blowingwith steam. The material was soluble in toluene and when applied from atoluene solution to glass fibre tape it dried (after removal of solvent)within a few hours of baking at 250 C. to a heat resistant tack-freeresin.

Other examples of organo-silicon compounds which may be polymerized tohigh molecular 7 weight compositions by treatment with sulphuric acidare the condensed hydrolysis products of ethyl silicon trichloride,.amyl silicon trichloride, diethyl silicon dichloride, diamyl silicondichloride, diphenyl silicon dichloride, phenylmethyldiethoxys'ilicane,etc. Beside these hydrolysis products, copolymers containing on theaverage of up to but not including three organic radicals per siliconatom may be polymerized in accordance with this invention. Thesecopolymers may 'be prepared by the cohydrolysis and cocondensation ofmixtures of differently substituted hydrolyzable silicanes obtained asproducts of the reaction of an organo-magnesium halide with silicontetrachloride or ethyl orthosilicate or by mixing diiferent silicanes togive mixtures of desired constituents in predetermined quantities. Amongthe silicanes employed to accomplish the latter were silicontetrachloride, ethylorthosilicate, methyltriethoxysilicane,dimethyldiethoxysilicane, trimethylethoxysilicane,phenylmethyldiethoxysilicane, phenyldimethylethoxysilicane,phenyltriethoxysilicane, diphenyldiethoxysilicane,ethyltriethoxysilicane, diethyl silicon dichloride, phenyl ethyl silicondichloride, butyltriethoxysilicane, dibutyldiethoxysilicane,benzyltriethoxysilicane, dibenzyldiethoxysilicane and others.

Our invention is applicable to any organosilicon oxide polymer having onthe average less than three organic radicals attached to each siliconatom through carbon atoms. The unusual properties of these polymers aredue primarily to the Si-O--Si groups present therein and to the or anicradicals attached to the silicon atoms. The kind and number of organicradicals attached to silicon do not afiect the fundamental behavior ofthe polymers, but only modify certain particular properties thereof.Besides the organic radicals already disclosed such radicals may bepresent as propyl, isopropyl, amyl, hexyl, heptyl to octadecyl andhigher; alicyclic radicals I such as cyclopentyl, cyolohexyl, etc.; aryland alkaryl radicals such as monoand poly-alkyl phenyls as tolyl, xylyl,mesityl, mono-, di-, and tri-ethyl phenyls, mono-, di-, and tri-propylphenyls, etc.; naphthyl, mono and poly-alkyl naphthyls as methylnaphthyl, diethyl naphthyls, tri-propyl naphthyl, etc.;tetra-hydro-naphthyl, anthracyl, etc.; araikyl such as benzyl,phenylethyl, etc. alkenyl such as methallyl, allyl, etc.

The new polymers may be used for various purposes. For example, they areexcellent coatings for metallic conductors and excellent impregnatingagents, particularly in the fabrication of electrical insulatingmaterials, because in their intermediate form they can be dissolved andapplied in the form of solutions for the impregnation of various fibrousmaterials and thereafter can be polymerized to complete insolubility andinfusibility. In the latter state they have good mechanicalcharacteristics and good electrical properties at room temperature, allof which are retained at temperatures above those at which prior coatingmaterials break down and deteriorate. The new polymers are relativelynon-flammable and are likewise superior to prior coatings in that underextreme conditions of temperature, etc. there is little tendency tocarbonize.

In making use of the new polymers for impreg nating tapes and otherfibrous materials for electrical insulation the polymerization iscarried out until the material has attained the sticky, viscousheat-convertible state just short of insolubility. Then, if desired, theacid may be removed by neutralization withalkali such as sodiumhydroxide within the scope of our invention may or calcium hydroxide.The alkali, when added in excess, also serves to remove impurities thatmay be present such as iron, etc. The neutralized product is dissolvedin toluene or other suitable solvent. The solution is applied bydipping, brushing or spraying, followed by evaporation of the solvent.Several applications of the solution may be. required to produce acoating of sufficient thickness. When the solvent has completelyevaporated, the coated article is baked for several hours at atemperature preferably between 200 C. and 300 C. until the viscouspolymeric mixture is converted to a tack-tree coating. With the phenylethyl silicone polymer, this condition is attained by baking for about36 hours while the temperature is slowly raised from about 200 C. toabout 260 C. Other organo-silicon polymers difierent temperatures andtimes, but such conditions are readily determined by trial.

In addition to the use 01' the new polymers in the field of electricalinsulation, there are many others for which these polymers at variousstages of polymerization are eminently adapted particularly in thosestages prior to heat convertibility. In these thermally stable stages,they may be used as hydraulic fluids, liquid insulating media, thermalexpansion fluids, waterproofing agents, etc. Their resistance to hightemperature, their electrical insulating properties, low freezing pointsand low vapor pressure adapt them to many diversified industrialapplications.

We claim:

1. The method of polymerizing a dehydrated liquid consisting of thedehydrated liquid polymeric diorganosiloxane in which each of the siliscon atoms of said siloxane has two and only two organic radicalsattached to each silicon atom, one of the two organic radicals attachedto each silicon atom being an alkyl radical and the other organicradical being selected from the class consisting of alkyl and arylradicals, which comprises adding sulphuric acid to said siloxane andmaintaining said acid in reactive relationship with said siloxane at atemperature below 250 C. until an increase in viscosity is effected.

2. The method of polymerizing a dehydrated liquid consisting of thedehydrated liquid polymeric diorganosiloxane in which each of thesilicon atoms of said siloxane has two and only two organic radicalsattached to each silicon atom, one of the two organic radicals attachedto each silicon atom being an alkyl radical and the other organicradical being selected from the class consisting of alkyl and arylradicals, which comprises adding sulphuric acid to said siloxane andmaintaining said acid in reactive relationship with said siloxane at atemperature between C. and 250 C. until an increase in viscosity iseffected.

3. The method of polymerizing a dehydrated liquid consisting of thedehydrated liquid polymeric dimethyl siloxane in which each of thesilicon atoms of said siloxane has two and only two methyl radicalsattached thereto, which comprises adding sulphuric acid to saidsiloxane, and maintaining said acid in reactive relationship with saidsiloxane at a temperature below 250 C. until an increase in viscosity iseifected.

4. The method of polymerizing a dehydrated liquid consisting of thedehydrated liquid polymeric dimethyl siloxane in which each of thesilicon atoms of said siloxane has two and only two methyl radicalsattached thereto, which comprises adding sulphuric acid to saidsiloxane, and

require ammo in reactive rela'timship with said siloxane at atemperature between 100 C. and 250 C. until an increase in vkcosity iseflected.

6.:The method of polymerizing a dehydrated liquid '0! the dehydratedliquid polymeric dibutyl siionne in which each of the silicon atoms atsaid silolane has two andonly two butyl radicak attached thereto, whichcomprises adding sulphuric acid to said siioxane and'main- 10 ammoniumThe following references are or record in the file of this patent:

UNITED STATE PATENTS Number Name Date 2258,220 Rochow Oct. 7, 19412,371,013 Rochow Har 8, 1945 roman rams-s Numbercountry Date 118,708Australia Sept. 4, 1941 Koton JL, Applied chem. ussa. vol. 12, pp.1435-9 (1939), as abstracted in Chemical Abstracts, pp. 8242-3, vol. 34,1900.

taining said acid in reactive relationship with said siloxane at a.temperature below 250C. until an increase in is eflected.

ROB ROY MCGREGOR.

1 1 8. Proceed. R0781 Society Imd... vol. 159, 1937. pp- 139 and 142. I

Robison. Tr. J. Chem. 500. 11m), '01. 105, 1914, cases 40 to 4'1.

Cusa, Proc; J. Chem. Soc. (Imdm); 1932. pages 2205 M2209.

